The present invention has been developed for incorporation in the type of automatic strapping machine in which a length of strap is guided in a chute around an article at a packaging station. Typically, the chute defines a generally rectangular opening in which the article is positioned during the strapping operation.
Means are provided in the chute for initially guiding and retaining the strap in the chute so that the strap cannot fall or be pulled inwardly against the article until after the loop has been formed. Typically, the chute is larger than the article to be strapped so as to accommodate various sizes of articles and thus, such strap guiding and retaining means function to initially maintain the strap in the largest possible loop configuration and, of course, function to permit the strap to be fed around the article without impinging upon or snagging upon the article.
After the strap loop has been formed, tension is applied to the strap to constrict the strap loop about the article and the overlapping strap ends are secured by conventional means. Various systems have been designed for permiting the strap to be released from the strap guiding and retaining means during the tensioning step so that the strap can be drawn tight against the article.
One type of system for initially guiding and retaining the strap in a chute is illustrated in the U.S. Pat. Nos. 3,572,237 and 3,536,430. These patents disclose an automatic strapping machine in which a yoke or chute defines a channel for receiving the strap and in which flexible flange members extend inwardly to overlie side portions of the strap and initially maintain the strap in the channel when the strap is fed in the chute around the article. Subsequently, when the strap is tensioned, the strap deforms the flexible flange members outwardly as the strap is pulled out of the channel and free of the flexible flange members into tight engagement around the article.
Another approach is disclosed in the U.S. Pat. Nos. 3,060,840 and 4,011,808. The apparatus described in these patents has a chute with a movable guide member defining a channel for receiving a strap or binding wire. During the initial step of feeding the strap or wire around the chute, the entire guide member is maintained in a closed position against a blocking member to cover the strap or wire receiving channel and to thereby prevent the strap or wire from leaving the channel. Subsequently, when the strap or wire is tensioned about the article, the guide member is moved to an open position spaced away from the blocking member to permit the strap or wire to be pulled out of the channel. In the machine disclosed in U.S. Pat. No. 3,060,840, the guide member is positively moved from the closed position to the open position by a hydraulic cylinder-piston actuator. In the apparatus disclosed in U.S. Pat. Nos. 4,011,808 the guide member is normally biased to the closed position and the tensioning of the strap overcomes the biasing mechanism to move the guide member to the open position for releasing the strap.
Finally, a common approach used today by a variety of manufacturers of automatic strapping machines employs rigid gate-type members which are normally biased closed over the strap guide channel during the feeding of the strap and which are opened in response to the tension on the strap when the strap is drawn tight about the article. Examples of this type of mechanism are shown in the U.S. Pat. Nos. 3,831,512; 3,889,585; and 3,899,963. In the machines disclosed in these patents, retainer gates are hingedly or pivotally mounted to the sides of the strap chute and have retaining flanges which are angled inwardly to overlie the strap receiving channel of the chute when the gates are in their normally biased-closed position. The tensioning of the strap forces the strap against the inwardly angled flanges of the gates and pivots the gates outwardly against the biasing means by an amount sufficient to permit release of the strap.
With the type of chute construction disclosed in the above-discussed U.S. Pat. Nos. 3,536,430 and 3,572,237, the flexible flange members are necessarily subjected to abrasion and flexing forces every time the strap is tensioned and pulled out of the chute. The components must thus be designed to withstand such abrasion and flexing. In addition, the flexible flange retaining members that cover the strap channel are exposed to the articles that are placed within the chute. Care must be taken to avoid inadvertent or accidental impingement of the flexible flange members by the article, by tools, or by other apparatus that may be present in, or used around, the strapping machine location.
It would be desirable to provide a strap chute design in which the strap retaining mechanism had a thickness, configuration, and composition that would readily withstand abrasion and pull-out forces imposed by the tensioning of the strap. Further, it would be advantageous if such an improved strap retaining mechanism had an increased capability for withstanding inadvertent impacts, misuse, and abuse which can occur from time to time under typical field conditions in which such automatic strapping machines are employed.
Although the approach employed in the apparatus disclosed in the above-discused U.S. Pat. Nos. 4,011,808 and 3,060,840 eliminates the need for exposed, flexible flange members, such apparatus requires a more complicated movable guide structure and mechanism for effecting the movement of the entire guide structure.
In contrast, the strap retaining systems disclosed in the above-discussed U.S. Pat. Nos. 3,831,512; 3,889,585; and 3,899,963 employ stationary guide channels and do not have exposed flexible flange members. However, such systems require the use of multi-piece hinge pin and spring biasing mechanisms which complicates the design and increases the manufacturing cost.
It would be desirable to provide an improved chute structure which could be rapidly assembled with fewer pieces and at less expense. Further, it would be desirable to provide such a structure in which the components could be relatively easily fabricated in predetermined lengths for accommodating a modular construction of the strap chute. A variety of different sizes of strap chutes could thus be assembled from a plurality of identical components.